Room: Track 3
We presented a novel tool of voxel-based dose-linear-energy-transfer (LET) volume histogram (DLVH) to present dose and LET information simultaneously in one plot. This tool was applied to patients experiencing adverse events in head and neck (H&N) cancer treated by intensity-modulated proton therapy (IMPT).
Physical dose and LET distributions were calculated using Monte Carlo simulations. DLVH was constructed with physical dose (in Gy[RBE]) and LET (in keV/µm) as two horizontal axes. The normalized volume of the structure was contoured as iso-volume lines in the dose-LET plane. Similar to dose-volume histogram indices such as Dv%, these iso-volume lines, DLv%, indicated the percentage volume v of a structure that had a dose of at least d Gy[RBE] and an LET of at least l keV/µm. All voxels in the structure were mapped into the dose-LET plane as dots to see how the dots with similar dose and LET were clustered. We included 20 head and neck (H&N) patients with unexpected adverse events (CTCAE grade=2) for analysis. The adverse event sites were contoured by the treating physicians and the corresponding DLVHs of the adverse event sites were generated and quantified to derive the voxel-wise dose-LET relationship in the adverse event regions.
Nine types of adverse events were observed in 20 patients and 23 adverse event regions were contoured. DLVHs exhibited highly correlated patterns between dose and LET. Dose played a dominant role for in-target adverse events such as hemorrhage and ulceration, while LET played an important role in out-of-target adverse events such as osteoradionecrosis and mucositis.
Our results suggest that dose and LET can contribute to adverse events in a combined and/or independent fashion. DLVH could be a powerful tool in predicting patient outcomes. Further study is underway to evaluate its use in plan evaluation to mitigate adverse events.
Funding Support, Disclosures, and Conflict of Interest: Supported by the National Cancer Institute Career Developmental Award K25-CA168984, by Arizona Biomedical Research Commission Investigator Award, by The Lawrence W. and Marilyn W. Matteson Fund for Cancer Research, and by The Kemper Marley Foundation.